groundwater saturation

シアトル近郊で起きた大規模な土砂崩れの原因が明らかにされました。

Washington landslide: 8 dead, 108 missing

A list of those reported missing following a landslide in rural Washington state includes 108 names, emergency officials said Monday.

But that doesn't mean all of them were killed in Saturday's disaster north of Seattle, Snohomish County Emergency Management Director John Pennington said.

The official death toll remains at eight with seven others hurt, he said.

Until Monday, the number of people unaccounted for was reported to be 18.

The landslide covered about a square mile and was caused by groundwater saturation tied to heavy rain in the area over the past month. It affected the towns of Oso, a remote community of about 180, and Darrington, a town of about 1,350.

Pennington said the slide over a weekend made it more of a challenge for rescuers since more people were apt to be home than on a weekday.

The affected area includes 35 traditionally built houses, 13 manufactured homes and RVs, and a cabin, Pennington said at a news conference. About half were occupied full time, while some others were vacation homes.

http://edition.cnn.com/2014/03/23/us/washington-landslide/index.html?hpt=hp_t3

原因はgroundwater saturation、「飽和地下水流」と見られています。もともと流れていた地下水の容量を越える大雨が地面から地下に流れた状態だということです。（cf. saturated groundwater） (Ume)